Treatment of sleep disordered breathing (SDB), such as obstructive sleep apnea (OSA), by continuous positive airway pressure (CPAP) flow generator systems involves the continuous delivery of air (or other breathable gas) pressurized above atmospheric pressure to the airways of a human or other mammalian patient via a conduit and a mask. Typically, the mask fits over the mouth and/or nose of the patient. Pressurized air flows to the mask and to the airways of the patient via the nose and/or mouth. As the patient exhales, carbon dioxide gas may collect in the mask. A washout vent in the mask or conduit discharges the exhaled gas from the mask atmosphere.
Known masks include a swivel elbow provided to the frame. The swivel elbow receives pressurized breathable gas from a suitable source of pressurized air. The leak rate through the swivel elbow forms part of the overall leak rate from the mask, incorporating the vent flow rate and the mask leak at the cushion of the mask. One key purpose of the vent flow rate is to provide sufficient CO2 washout from the mask. It is advisable to control the flow rate from the mask in order to provide constant known characteristics to the flow generator for prediction of pressure, flow and leakage from the cushion of the mask. Excessive leakage from the swivel elbow may also lead to noise and disturbance to the patient.